The effect of the infant's temperament on its caregiver is investigated. One study involves investigation of maternal and infant behaviors in an American middle class sample at one and three months of age, in order to further compare with the Japanese data obtained by previous researchers and also to understand how infant's temperament affects maternal behavior in early infancy. A second study is designed to investigate the nature of peer and teacher-infant interaction during the second and third quarter of the second year and the first half of the fourth year in the day care situation and to monitor these changes according to the developmental stage of the infant.